


Aliens and Wizards (Former)

by stickers_on_a_laptop



Series: CM Crossovers [4]
Category: 30歳まで童貞だと魔法使いになれるらしい | 30-sai Made Doutei da to Mahou Tsukai ni Nareru Rashii (TV), Kamen Rider Build
Genre: Beach Episode, Crack Treated Seriously, Fluff and Crack, M/M, am i seriously the first build crossover?, here i am with another crossover
Language: English
Status: Completed
Published: 2020-12-31
Updated: 2020-12-31
Packaged: 2021-03-11 04:00:38
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 3,492
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28458675
Author URL: https://archiveofourown.org/users/stickers_on_a_laptop/pseuds/stickers_on_a_laptop
Summary: Kurosawa and Adachi have to spend time with Adachi's cousin
Relationships: Adachi Kiyoshi/Kurosawa Yuichi, Banjou Ryuuga/Kiryuu Sento
Series: CM Crossovers [4]
Series URL: https://archiveofourown.org/series/2080068
Comments: 10
Kudos: 60





	1. Surprise Family Reunion

**Author's Note:**

> Beta-ed by the wonderful creativityobsessed!!

Kurosawa, reading the latest edition of Ragna Crimson with Adachi’s head in his lap, was startled when Adachi moved to get his ringing phone. He pouted when Adachi left the couch, watching as he moved to the kitchen to get some privacy. 

“Hello mom?” was all Kurosawa heard before going back to his manga, which was getting exciting. He lost himself in the characters before Adachi came back, scowling a bit. 

“Kiyoshi? What’s wrong?” Kurosawa asked, putting the book face down on the coffee table. 

“My mom said my cousin is coming to Tokyo, and since we’re the only family he has left now, my mom said I had to be nice and show him around. She also said we should let him stay here instead of letting him stay in a hotel” Adachi grumbled. 

“What’s your cousin like?” Kurosawa asked, pulling Adachi into his arms and playing with his hair.

“What I remember personally is that he’s seven years younger than me and was the world’s fiestiest two-year old when he came over when I was nine. But there are some weird rumors about him? His parents died when he was thirteen though and then he kinda disappeared until he was apparently framed for murder” Adachi said.

“Framed for murder??”

“He was innocent, but it was some family gossip for a while. I haven’t seen him since I was like eleven, and everyone said we look alike, but I’m not sure how true it is, a lot of the murder stuff was hushed up soon after” Adachi explained. 

“When is he supposed to come?” Kurosawa asked, thinking they would have to clean up a bit to get their apartment ready.

“My mom said he’s bringing a friend, too” Adachi said, crossing his arms and sighing. 

“Okay, when are they coming?”

“In like two days” 

“So…perfect timing then” Kurosawa said.

Adachi pouted. “We were supposed to have the time off for ourselves, not having to deal with family”

“Hey, we can always ditch them at the beach and whatnot” Kurosawa said, smiling mischievously. 

“But we won’t be able to do this” Adachi said, leaning in for a kiss, taking Kurosawa’s breath away.

“Then we should do it while we can” Kurosawa murmured, adjusting himself as Adachi settled on top of him.

* * *

“Coming!” Kurosawa called as the doorbell rang incessantly. It was nearly two hours later than the expected time of arrival for Adachi’s cousin and his friend, and Kurosawa was slightly annoyed since they had not received a warning that they would be late. 

“Hell-” Kurosawa stopped in his tracks when he saw who clearly had to be Adachi’s cousin. 

“Took you long enough” the cousin said, coming in without permission and looking over the apartment, not bothering to take off his shoes.

“Can you please take off your shoes?” Kurosawa asked, trying to breathe normally. 

“Yes, we can, sorry, we’re used to keeping our shoes on in the lab and cafe. I’m Kiryuu Sento, this idiot’s boyfriend. Feel free to call me Sento, everyone does” the other young man said, bending down to take off his two different colored high-tops. 

“Who are you calling an idiot?” Adachi’s cousin asked, coming over to take his boots off. 

“You, Banjou Ryuuga” Sento said. 

Banjou seemed ready to swing when Adachi came out from the other room, where he had been rearranging the sleeping conditions for his cousin and “friend”.

Everyone froze as Adachi and Banjou saw each other for the first time. 

“What the hell??” Banjou asked, coming up to Adachi to look at him, one shoe still on. 

Kurosawa took in the scene. There was Adachi, looking from Banjou to Sento to Kurosawa, while Banjou was just staring at Adachi. 

“Your mom didn’t say you look exactly like me but with black hair” Banjou said after a few seconds. 

“She didn’t tell me either, but I guess the gossip about us looking like our grandfather is true” Adachi countered, his eyes clearly taking in Banjou’s identical-ness. 

Kurosawa couldn’t believe how much the two cousins looked alike, even with a seven year difference and Banjou’s hair being brown and up in three braids. The way they were dressed was different as well, with Adachi in his hoodie and Banjou wearing a t-shirt over a long sleeve and a flannel button down around his waist. But their height was the same, they had the same mole near their lip, and currently the same bewildered expression. 

“Wild...your human DNA really came through here, Banjou” Sento said after looking back and forth from his boyfriend to Adachi. 

Kurosawa didn’t feel like trying to figure out that sentence in the slightest. 

* * *

“So you haven’t been in Tokyo in how many years?” Kurosawa asked while they were eating dinner. Banjou had found the one instant noodle bowl in the house and made it, sitting on the kitchen counter instead of at the table with the other three. (Sento had apologized while Banjou just glared and dared anyone to defy him).

“Since whenever I saw him last for me” Banjou said, pointing to Adachi with his chopsticks. 

“Saving Earth kind of meant I lost track of time for me” Sento shrugged. 

Kurosawa exchanged a glance with Adachi, the two of them silently agreeing they weren’t going to press the issue. 

“What do you guys do?” Kurosawa asked instead. 

“I’m a physicist and that musclebrain is a martial arts fighter” Sento explained. 

“What about you ossans?” Banjou asked around a mouthful of noodles.

Kurosawa didn’t know what face he made but it made Adachi giggle, so it was worth it. 

“We work for a stationary company” Adachi explained after a drink of water. 

“And you met there? Your mom didn’t seem to be aware we were boyfriends, Adachi-san, but she said you had a nice boyfriend of your own” Sento said. 

“Yes, we met there and got together last year” Kurosawa said, not wanting Adachi to have to explain. 

“So you’ve been together about the same length we have” Sento said thoughtfully. 

Banjou made a face. “Who’s with you?

“You are, last time I checked” Sento shot back, rolling his eyes. 

Kurosawa raised his eyebrows, a little unsure with how to deal with the two of them, especially considering they would be staying for a few days. At least Sento seemed friendly enough, while Banjou might be a tougher nut to crack. Kurosawa couldn’t get over how much he looked like Adachi, yet how different in personality they were. 

* * *

Later, in bed, Kurosawa asked Adachi how he was holding up. 

“Better than I thought. He hasn’t changed that much honestly” Adachi said, looking thoughtful in the dim lighting. 

“Is there anything you think I should know?” Kurosawa asked, not wanting to pry but wanting to be prepared. 

Adachi hummed, thinking. “There are rumors he was watched a lot by scientists as a kid, but remember I didn’t see him a lot. What I remember about him is….embarrassing, since people were always bringing it up at family reunions and stuff” 

“Oh?” 

Adachi hid his face in Kurosawa’s chest as he explained the story he remembered best, causing Kurosawa to try and hide his laughs. 

“Sounds like something I shouldn’t bring up with Banjou-kun, then” Kurosawa said when he calmed himself. 

“I think he would punch you” Adachi said honestly. 

“I think you’re right” 

“C’mon, let’s get some sleep” Adachi said, turning off the lights before snuggling into Kurosawa. 

“Okay” Kurosawa said, dropping a kiss on Adachi’s head and pulling him close. 

**Notes for the Chapter:**

> So the story I had in mind was that Banjou, age 3-4, decided to just......bite Adachi's butt at a family reunion, unprovoked, when Adachi was just reading on the floor (based on a true story that is indeed told over and over)


	2. Ossans at the Amusement Park

**Summary for the Chapter:**

> The four of them go to a familiar theme park

The next morning, when Kurosawa was making breakfast, Banjou and Sento came out of the guest room, Banjou’s hair extremely fluffy since he’d taken out the braids. 

“Good morning” Kurosawa said, looking up from the tamagoyaki he was making.

“Good morning” Sento said, while Banjou looked too sleepy to say anything. Sento guided his boyfriend to a chair and started combing Banjou’s hair, expertly braiding the hair the way Banjou had it the day before. Kurosawa smiled at the scene, thinking about how Adachi was like that in the mornings as well: usually too tired to talk.

“Sento-kun, can you tell Adachi that breakfast is ready?” Kurosawa asked when he was done with the tamagoyaki.

Sento nodded and went off to get Adachi while Banjou watched Kurosawa set the table. 

“Did you sleep well?” Kurosawa asked lightly.

Banjou made a face but nodded, clearly not wanting to talk.

When Adachi and Sento came to the table, the four of them said thanks and started eating. Sento enjoyed the tamagoyaki, while Banjou made a face when he found out it was sweet. Since they had plans to go to the amusement park, they didn’t linger over breakfast, instead hurrying to get to the train station. 

* * *

“Kurosawa-san! Adachi-san!” Rokkaku’s voice carried through the morning air, causing Kurosawa to close his eyes so he could face his younger coworker. 

“Adachi-san, you have a twin?” Rokkaku asked when he saw Banjou. 

“No, he’s my younger cousin, we take after our grandfather” Adachi explained.

Rokkaku nodded seriously and watched Banjou and Sento, who were ignoring each other as they played some game on their phones back to back.

“Adachi-san, are they boyfriends?” Rokkaku asked in a quiet voice. 

Kurosawa started coughing. How in the-?

Adachi looked like he wanted to melt into the ground as he looked around and nodded. 

“I knew it!” Rokkaku burst into a grin. “Oh! There’s my train! Man, I didn’t know you two were close enough to spend your days off together! Invite me next time!” he said as he left. 

“Who was that?” Banjou asked when Rokkaku was gone. 

“Our coworker” Kurosawa answered, still in disbelief. Even though Rokkaku was long gone, he kept staring at where Rokkaku had left. 

“Our train, Kurosawa” Adachi tugged on Kurosawa’s sleeve to get him moving. 

“Hmm? Oh, sorry” Kurosawa said, getting on the train, where he contemplated everything in his life that had let up to that moment. How Rokkaku could see that Banjou and Sento were boyfriends (doing something that could just be seen as friends, no less) after three seconds but not him and Adachi after nearly a year was beyond him. He could see Adachi silently watching him, and wished he could take his hand, but Adachi still wasn’t quite there yet for such big crowds and holding hands. But he was fine, and once they were off the train, he reassured Adachi he was fine, just concerned for Rokkaku, which made Adachi smile, the one that Kurosawa privately called “blinding.” 

* * *

“Well, here we are” Kurosawa said when they entered the amusement park, the same one he had gone to with Adachi nearly a year ago now. “Are you guys going to want to stick with us? We don’t really do the roller coasters or anything” 

Banjou was looking at everything, a grin on his face that told Kurosawa he was very pleased. Sento was watching him, his scarf blowing in the wind. 

“Kurosawa, let’s do the teacups” Adachi suggested. Kurosawa nodded, a little surprised when Banjou and Sento followed them. 

One short wait later, the two of them were in their teacup, chatting, while Banjou was making his and Sento’s go to the utter limit. Kurosawa couldn’t help but laugh at Adachi’s slightly stunned expression, pulling out his phone to take pictures and a video. Once the ride was over, the two of them had to support Banjou and Sento, who were dizzy out of their minds. 

“If you guys are looking for more exciting rides, then you might want to leave us now” Kurosawa warned, knowing that Adachi would want to avoid fainting again. 

“What are you going on next?” Sento asked,

“The carousel” Adachi said, which made Banjou make a face and go off towards the roller coaster. Sento rolled his eyes. 

“Shall we meet in front of the teacups in like...two hours or so then?” he asked.

Kurosawa checked his watch and nodded. “Sounds good Sento-kun”

Sento nodded and chased after Banjou, calling him an “impatient musclebrain”, causing Kurosawa to smirk. 

“He’s nothing like me” Adachi said as he watched the two of them go. 

“That’s okay” Kurosawa said, guiding Adachi to the carousel and letting Adachi put him on the hippo this time. 

* * *

The two hours seemed to fly by and when they met up with Sento and Banjou, the two of them were clearly having the time of their lives, judging by their grins and Sento’s messed up hair. Despite Adachi saying that he and Banjou were nothing alike other than in looks, they got the same energy drink and a chocolate crepe when they were finished with lunch, which Kurosawa pointed out. They agreed to split up again and meet in another two hours, after which they would leave the park. 

After about half an hour, Kurosawa was ready to leave, but even if Adachi had wanted to leave as well, they had to wait for Banjou and Sento. But when Adachi took him to the water gun ride for the third time, Kurosawa still took a lot of pictures and smiled at Adachi’s face, which had the biggest grin. 

“This is fun, Yuichi” Adachi said quietly when they both decided they had had enough and were waiting for the other two, holding ice creams that were rapidly melting. 

“Even though you had to bring along your cousin?” Kurosawa teased. 

“The one that calls you ossan?” Adachi smirked, which did things to Kurosawa. Ever since Adachi had grown bolder, sometimes Kurosawa would regret teasing him. 

“You guys  _ are  _ ossans” Banjou said, startling Kurosawa before composing himself. 

“We’re thirty-one” Kurosawa said. 

“And that’s older than Kazumin, who is  _ also  _ an ossan, so…” Banjou said. 

Sento whispered something into Banjou’s ear that made him glance down before turning around in embarrassment, making Sento smirk. 

Kurosawa wasn’t entirely sure what had just happened but decided to let it go. They would only be here for a few more days.

**Notes for the Chapter:**

> Man, I love Rokkaku


	3. Beaches and Freckles

**Summary for the Chapter:**

> The Beach Episode!

While Kurosawa wouldn’t say the next two days went swimmingly, they also weren’t the worst days of his life. Banjou seemed to find it hilarious that Kurosawa wasn’t used to being called “ossan” (although Sento said he was really bad with honorifics in general), insisted on eating instant ramen whenever he could (Kurosawa didn’t understand that one), and often forgot to take off his shoes. But he was also able to keep up with Adachi on Super Smash Bros on the Switch, absolutely destroying Kurosawa with a “sixth sense” he claimed he had. Since neither Kurosawa nor Adachi were interested in sports, he went to the gym for a few hours in the morning and in the evening. Sento, on the other hand, often spent time tinkering with random devices around the house, making them work a lot better than Kurosawa ever could have imagined, sometimes with Banjou goading him, sometimes not. 

* * *

When it was finally Thursday, Kurosawa was ready for them to leave after their beach trip. 

“Are you ready for the beach, Adachi?” Kurosawa asked as they waited for the bus. 

“I hope so, I haven’t been in years” Adachi answered honestly, looking adorable in the bucket hat Minato had given him last year when they had all been watching his concert and Adachi had gotten sunburned. 

Banjou watched them in slight amusement, Kurosawa noticed. 

“Have you guys been to the beach recently?” he asked.

“For fun? No. To fight stupid evil aliens? Yes” Banjou said, dodging Sento’s punch to the arm. 

“I mean you’re a stupid alien” Sento said. 

Banjou made a face and picked up the basket they had packed, since the bus had arrived, ignoring Sento as he got on. 

Once on the bus, Kurosawa pulled out his phone.

**Why does Sento-kun keep calling Banjou-kun an alien?** He texted Adachi. 

**Probably related to the fact that his mom was supposedly only pregnant with him for two months** Adachi replied. 

Kurosawa looked at Adachi, then remembered the powers Adachi had gotten rid of. He quirked his eyebrows, wondering what the heck he had “married” into. (One day, he was going to get rings. For now, the pens were enough).

**Did you know about that?** Kurosawa couldn’t help but ask.

**Just rumors when I was a kid, then this last year was kind of crazy, remember?** Adachi looked at him, shrugging. 

Kurosawa couldn’t help but melt at Adachi’s earnest face. He put his foot near Adachi’s, glad that he could no longer hear the sappy thoughts he was thinking. 

* * *

“Wow, it’s bright here” Banjou said once they were off the bus, forty-five minutes later. Sento handed him a pair of sunglasses. 

They found a spot on the beach that wasn’t too crowded and set down their stuff. Banjou immediately took off his shirt and rolled up his pants, ready to be in the water. Sento took off his shirt as well, and the two of them ran off, not bothering to help set up anything. 

“I guess it’s up to us ossans” Adachi joked, picking up Banjou’s shirt and folding it the way Kurosawa had taught him, then doing the same with Sento’s. 

“Are you going to want to go in the water?” Kurosawa asked.

“Of course” Adachi answered, looking a little insulted. 

“Just making sure” Kurosawa reassured him, looking around and pressing a quick kiss to Adachi’s forehead when he determined no one was looking. 

“Yuichi” Adachi complained. 

“What’s the matter, Kiyoshi?” Kurosawa asked, enjoying Adachi’s flustered look. 

Adachi just shook his head and kicked off his shoes to go into the water, Kurosawa following right behind him. 

* * *

After being in the water for a while, finding crabs, and making sand castles in the sun, Kurosawa was ready to eat the sandwiches he had made. Adachi called his cousin and Sento, the two of them drenched. Kurosawa handed them towels, Sento putting his around his shoulders while Banjou just set it down. 

“You guys having fun?” Kurosawa asked. 

Banjou nodded as he took a banana out of the picnic basket, his hair stuck to his forehead. Kurosawa watched as Sento teased Banjou, only for Banjou to point out that Sento’s hair was even wilder. The two of them started pushing each other, but it never got out of hand, and when they were done eating, they went back to the water. 

“Do you want to go back in the water?” Adachi asked.

“Not really, but if you want to, go ahead” Kurosawa saw how Adachi was looking longingly at the water and smiled at him to show he didn’t mind. 

“If you’re sure” Adachi said, before running off to join his cousin and cousin’s boyfriend. 

Kurosawa watched as Adachi allowed himself to get soaked by Banjou’s antics before falling asleep under the warm sun. 

* * *

“Hey, Kurosawa-san! Get up! Your boyfriend cut himself when a wave knocked him over” Kurosawa was roughly awakened by Banjou, who was shaking him. If the sun was anything to go by, it was about two hours later.

“Is he okay?” Kurosawa asked, feeling slightly panicked. 

“I’m FINE” Adachi said, looking annoyed as he walked over, walking on tip toes since his ankle had a slightly bleeding cut on it. 

“Still, we don’t want it to get infected” Kurosawa tutted, bringing out the first aid kit he had brought just in case. 

Banjou, satisfied that his cousin was in good hands if his face was anything to go by, sat down. Sento, who had been watching from the sidelines, sat down next to Banjou. 

“You called him Kurosawa-san” Kurosawa heard as he dried off Adachi’s ankle. 

“Dang it!!!!!” Banjou cried. 

Adachi looked over at his cousin before focusing on Kurosawa. 

“Are those...freckles?” Adachi asked as the band-aid went on. 

“Hmm? Oh...yeah I get them easily” Kurosawa explained. 

“I’ve never noticed” Adachi said, wonderingly. 

“If you guys are ready to leave, we’re okay with that” Banjou said, interrupting whatever thought Kurosawa was having. 

“Help me pack up then” Kurosawa said, standing up and offering his hand to Adachi, who took it. 

The four men got all their stuff ready and went to the bus stop. 

“You guys are all packed to leave when we get back?” Kurosawa asked.

“You want to get rid of us that easily?” Banjou asked with a smirk. 

Sento rolled his eyes. “Like you don’t want to go see Sawa and Misora and everyone” 

Banjou crossed his arms and pouted, which Kurosawa took to mean “you’re right but I won’t admit it”. 

* * *

“Well, they’re finally gone” Adachi said when Banjou and Sento had left. 

“What do you want to do, then?” Kurosawa asked, feeling breathless when Adachi looked at him. 

Adachi stepped closer and closer until Kurosawa was pinned against the wall.

“I want to kiss every single freckle” Adachi whispered, looking slightly mischievous.

“Might take a while, so good thing we have another few days off” Kurosawa whispered back, smiling as Adachi started making good on his words. 

**Notes for the Chapter:**

> Machida Keita with freckles >>>


End file.
